Salinity effects on germination, growth, and seed production of the halophyte Cakile maritima

Cakile maritima (Brassicaceae) is a halophyte that thrives on dunes along the Tunisian seashore. Besides its ecological interest for soil fixation, this plant produces seeds rich in lipids (40% on dry weight basis), making it a potential source of oil for industrial use. The purpose of the present work was to study the salt tolerance of this species at germination, vegetative growth and fruiting stages. NaCl inhibited germination only at concentrations higher than 200 mM, mainly by an osmotic effect (fully reversible after seed transfer to water). At the vegetative stage, the plant exhibited a typical halophytic behaviour, requiring the presence of a moderate salt concentration (50 to 100 mM NaCl) to express its maximal growth potentialities. Growth activity was maintained up to 500 mM NaCl. Salt tolerance of C maritima at the vegetative stage seemed to be mainly based on: (i) the capacity to preserve the biomass production within the range of optimal salt concentrations; (ii) the ability to maintain the tissue water status; and (iii) the efficiency of selective K+ uptake, in spite of high Na+ concentration in the medium. Indirect evidence of Na+ utilisation by the plant for osmotic adjustment was obtained. Seed production was stimulated at 50 to 100 mM NaCl as compared to control treatment, and severely restricted at higher salt levels. Individual seed mass was moderately diminished by increasing NaCl concentrations.